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  • richardmitnick 12:07 pm on January 15, 2019 Permalink | Reply
    Tags: , Bayesian modeling, Democratizing data science, MIT   

    From MIT News: “Democratizing data science” 

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    From MIT News

    January 15, 2019
    Rob Matheson

    1
    MIT researchers are hoping to advance the democratization of data science with a new tool for nonprogrammers that automatically generates models for analyzing raw data. Image: Christine Daniloff, MIT

    Tool for nonstatisticians automatically generates models that glean insights from complex datasets.

    MIT researchers are hoping to advance the democratization of data science with a new tool for nonstatisticians that automatically generates models for analyzing raw data.

    Democratizing data science is the notion that anyone, with little to no expertise, can do data science if provided ample data and user-friendly analytics tools. Supporting that idea, the new tool ingests datasets and generates sophisticated statistical models typically used by experts to analyze, interpret, and predict underlying patterns in data.

    The tool currently lives on Jupyter Notebook, an open-source web framework that allows users to run programs interactively in their browsers. Users need only write a few lines of code to uncover insights into, for instance, financial trends, air travel, voting patterns, the spread of disease, and other trends.

    In a paper [ACM Digital Library] presented at this week’s ACM SIGPLAN Symposium on Principles of Programming Languages, the researchers show their tool can accurately extract patterns and make predictions from real-world datasets, and even outperform manually constructed models in certain data-analytics tasks.

    “The high-level goal is making data science accessible to people who are not experts in statistics,” says first author Feras Saad ’15, MEng ’16, a PhD student in the Department of Electrical Engineering and Computer Science (EECS). “People have a lot of datasets that are sitting around, and our goal is to build systems that let people automatically get models they can use to ask questions about that data.”

    Ultimately, the tool addresses a bottleneck in the data science field, says co-author Vikash Mansinghka ’05, MEng ’09, PhD ’09, a researcher in the Department of Brain and Cognitive Sciences (BCS) who runs the Probabilistic Computing Project. “There is a widely recognized shortage of people who understand how to model data well,” he says. “This is a problem in governments, the nonprofit sector, and places where people can’t afford data scientists.”

    The paper’s other co-authors are Marco Cusumano-Towner, an EECS PhD student; Ulrich Schaechtle, a BCS postdoc with the Probabilistic Computing Project; and Martin Rinard, an EECS professor and researcher in the Computer Science and Artificial Intelligence Laboratory.

    Bayesian modeling

    The work uses Bayesian modeling, a statistics method that continuously updates the probability of a variable as more information about that variable becomes available. For instance, statistician and writer Nate Silver uses Bayesian-based models for his popular website FiveThirtyEight. Leading up to a presidential election, the site’s models make an initial prediction that one of the candidates will win, based on various polls and other economic and demographic data. This prediction is the variable. On Election Day, the model uses that information, and weighs incoming votes and other data, to continuously update that probability of a candidate’s potential of winning.

    More generally, Bayesian models can be used to “forecast” — predict an unknown value in the dataset — and to uncover patterns in data and relationships between variables. In their work, the researchers focused on two types of datasets: time-series, a sequence of data points in chronological order; and tabular data, where each row represents an entity of interest and each column represents an attribute.

    Time-series datasets can be used to predict, say, airline traffic in the coming months or years. A probabilistic model crunches scores of historical traffic data and produces a time-series chart with future traffic patterns plotted along the line. The model may also uncover periodic fluctuations correlated with other variables, such as time of year.

    On the other hand, a tabular dataset used for, say, sociological research, may contain hundreds to millions of rows, each representing an individual person, with variables characterizing occupation, salary, home location, and answers to survey questions. Probabilistic models could be used to fill in missing variables, such as predicting someone’s salary based on occupation and location, or to identify variables that inform one another, such as finding that a person’s age and occupation are predictive of their salary.

    Statisticians view Bayesian modeling as a gold standard for constructing models from data. But Bayesian modeling is notoriously time-consuming and challenging. Statisticians first take an educated guess at the necessary model structure and parameters, relying on their general knowledge of the problem and the data. Using a statistical programming environment, such as R, a statistician then builds models, fits parameters, checks results, and repeats the process until they strike an appropriate performance tradeoff that weighs the model’s complexity and model quality.

    The researchers’ tool automates a key part of this process. “We’re giving a software system a job you’d have a junior statistician or data scientist do,” Mansinghka says. “The software can answer questions automatically from the data — forecasting predictions or telling you what the structure is — and it can do so rigorously, reporting quantitative measures of uncertainty. This level of automation and rigor is important if we’re trying to make data science more accessible.”

    Bayesian synthesis

    With the new approach, users write a line of code detailing the raw data’s location. The tool loads that data and creates multiple probabilistic programs that each represent a Bayesian model of the data. All these automatically generated models are written in domain-specific probabilistic programming languages — coding languages developed for specific applications — that are optimized for representing Bayesian models for a specific type of data.

    The tool works using a modified version of a technique called “program synthesis,” which automatically creates computer programs given data and a language to work within. The technique is basically computer programming in reverse: Given a set of input-output examples, program synthesis works its way backward, filling in the blanks to construct an algorithm that produces the example outputs based on the example inputs.

    The approach is different from ordinary program synthesis in two ways. First, the tool synthesizes probabilistic programs that represent Bayesian models for data, whereas traditional methods produce programs that do not model data at all. Second, the tool synthesizes multiple programs simultaneously, while traditional methods produce only one at a time. Users can pick and choose which models best fit their application.

    “When the system makes a model, it spits out a piece of code written in one of these domain-specific probabilistic programming languages … that people can understand and interpret,” Mansinghka says. “For example, users can check if a time series dataset like airline traffic volume has seasonal variation just by reading the code — unlike with black-box machine learning and statistics methods, where users have to trust a model’s predictions but can’t read it to understand its structure.”

    Probabilistic programming is an emerging field at the intersection of programming languages, artificial intelligence, and statistics. This year, MIT hosted the first International Conference on Probabilistic Programming, which had more than 200 attendees, including leading industry players in probabilistic programming such as Microsoft, Uber, and Google.

    “My team at Google AI builds probabilistic programming tools on top of TensorFlow. Probabilistic programming is an important area for Google, and time series modeling is a promising application area, with many use cases at Google and for Google’s users,” says Ryan M. Rifkin ’94, SM ’97, PhD ’02, a Google researcher who was not involved in the research. The researchers’ paper “shows how to apply probabilistic programming to solve this important problem — and reduces the effort needed to get started, by showing how the probabilistic programs can be synthesized from data, rather than written by people.”

    See the full article here .


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  • richardmitnick 3:04 pm on January 9, 2019 Permalink | Reply
    Tags: , , , , , MIT, , The findings are the first evidence that the corona shrinks as a black hole feeds or accretes   

    From MIT News: “Astronomers observe evolution of a black hole as it wolfs down stellar…” 

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    From MIT News

    January 9, 2019
    Jennifer Chu

    1
    X-ray echoes, mapped by NASA’s Neutron star Interior Composition Explorer (NICER), revealed changes to the accretion disk and corona of black hole MAXI J1820+070.
    Image: NASA’s Goddard Space Flight Center

    NASA/NICER

    …Halo of highly energized electrons around the black hole contracts dramatically during feeding frenzy.

    On March 11, an instrument aboard the International Space Station detected an enormous explosion of X-ray light that grew to be six times as bright as the Crab Nebula, nearly 10,000 light years away from Earth. Scientists determined the source was a black hole caught in the midst of an outburst — an extreme phase in which a black hole can spew brilliant bursts of X-ray energy as it devours an avalanche of gas and dust from a nearby star.

    Now astronomers from MIT and elsewhere have detected “echoes” within this burst of X-ray emissions, that they believe could be a clue to how black holes evolve during an outburst. In a study published today in the journal Nature, the team reports evidence that as the black hole consumes enormous amounts of stellar material, its corona — the halo of highly-energized electrons that surrounds a black hole — significantly shrinks, from an initial expanse of about 100 kilometers (about the width of Massachusetts) to a mere 10 kilometers, in just over a month.

    The findings are the first evidence that the corona shrinks as a black hole feeds, or accretes. The results also suggest that it is the corona that drives a black hole’s evolution during the most extreme phase of its outburst.

    “This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution,” says Jack Steiner, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself.”

    Steiner’s MIT co-authors include Ronald Remillard and first author Erin Kara.

    X-ray echoes

    The black hole detected on March 11 was named MAXI J1820+070, for the instrument that detected it. The Monitor of All-sky X-ray Image (MAXI) mission is a set of X-ray detectors installed in the Japanese Experiment Module of the International Space Station (ISS), that monitors the entire sky for X-ray outbursts and flares.

    Soon after the instrument picked up the black hole’s outburst, Steiner and his colleagues started observing the event with NASA’s Neutron star Interior Composition Explorer, or NICER, another instrument aboard the ISS, which was designed partly by MIT, to measure the amount and timing of incoming X-ray photons.

    “This boomingly bright black hole came on the scene, and it was almost completely unobscured, so we got a very pristine view of what was going on,” Steiner says.

    A typical outburst can occur when a black hole sucks away enormous amounts of material from a nearby star. This material accumulates around the black hole, in a swirling vortex known as an accretion disk, which can span millions of miles across. Material in the disk that is closer to the center of the black hole spins faster, generating friction that heats up the disk.

    “The gas in the center is millions of degrees in temperature,” Steiner says. “When you heat something that hot, it shines out as X-rays. This disk can undergo avalanches and pour its gas down onto the central black hole at about a Mount Everest’s worth of gas per second. And that’s when it goes into outburst, which usually lasts about a year.”

    Scientists have previously observed that X-ray photons emitted by the accretion disk can ping-pong off high-energy electrons in a black hole’s corona. Steiner says some of these photons can scatter “out to infinity,” while others scatter back onto the accretion disk as higher-energy X-rays.

    By using NICER, the team was able to collect extremely precise measurements of both the energy and timing of X-ray photons throughout the black hole’s outburst. Crucially, they picked up “echoes,” or lags between low-energy photons (those that may have initially been emitted by the accretion disk) and high-energy photons (the X-rays that likely had interacted with the corona’s electrons). Over the course of a month, the researchers observed that the length of these lags decreased significantly, indicating that the distance between the corona and the accretion disk was also shrinking. But was it the disk or the corona that was shifting in?

    To answer this, the researchers measured a signature that astronomers know as the “iron line” — a feature that is emitted by the iron atoms in an accretion disk only when they are energized, such as by the reflection of X-ray photons off a corona’s electrons. Iron, therefore, can measure the inner boundary of an accretion disk.

    When the researchers measured the iron line throughout the outburst, they found no measurable change, suggesting that the disk itself was not shifting in shape, but remaining relatively stable. Together with the evidence of a diminishing X-ray lag, they concluded that it must be the corona that was changing, and shrinking as a result of the black hole’s outburst.

    “We see that the corona starts off as this bloated, 100-kilometer blob inside the inner accretion disk, then shrinks down to something like 10 kilometers, over about a month,” Steiner says. “This is the first unambiguous case of a corona shrinking while the disk is stable.”

    “NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before,” Kara adds. “Previously these light echoes off the inner accretion disk were only seen in supermassive black holes, which are millions to billions of solar masses and evolve over millions of years. Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human time scales.”

    While it’s unclear what is exactly causing the corona to contract, Steiner speculates that the cloud of high-energy electrons is being squeezed by the overwhelming pressure generated by the accretion disk’s in-falling avalanche of gas.

    The findings offer new insights into an important phase of a black hole’s outburst, known as a transition from a hard to a soft state. Scientists have known that at some point early on in an outburst, a black hole shifts from a “hard” phase that is dominated by the corona’s energy, to a “soft” phase that is ruled more by the accretion disk’s emissions.

    “This transition marks a fundamental change in a black hole’s mode of accretion,” Steiner says. “But we don’t know exactly what’s going on. How does a black hole transition from being dominated by a corona to its disk? Does the disk move in and take over, or does the corona change and dissipate in some way? This is something people have been trying to unravel for decades And now this is a definitive piece of work in regards to what’s happening in this transition phase, and that what’s changing is the corona.”

    This research is supported, in part, by NASA through the NICER mission and the Astrophysics Explorers Program.

    See the full article here .


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  • richardmitnick 11:38 am on January 9, 2019 Permalink | Reply
    Tags: Anthony Badea, , , , , MIT, ,   

    From MIT News: “Achieving goals in the lab and on the pitch” Anthony Badea 

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    From MIT News

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    Anthony Badea. Image: Ian MacLellan

    January 9, 2019
    Gina Vitale

    Senior Anthony Badea, a physics major and varsity soccer player, investigates the beginnings of the universe.

    Anthony Badea got hooked on physics during his senior of high school in Irvine, California. He used to fall asleep watching interviews and speeches by public figures in science like astrophysicist Neil deGrasse Tyson and string theorist Michio Kaku. The questions they asked about the universe fascinated him.

    When he came to MIT, Badea found himself in awe of another scientist — the one who taught 8.03 (Waves and Vibrations). That was Yen-Jie Lee, the Class of 1958 Career Development Associate Professor of Physics and a researcher in the Laboratory for Nuclear Science.

    “I just thought he was the coolest person I’ve ever met,” Badea says. “He comes in front of the class, and he’s super energetic about everything. Everyone in the class loves him.”

    Badea, now majoring in both physics and mathematics and minoring in statistics, reached out to Lee inquiring about his research with CERN. When Lee explained his work, it was so advanced that Badea understood almost nothing — but he was thrilled to have the chance to learn. He’s been a part of the MIT Relativistic Heavy Ion Group ever since.

    “There’s a graduate student area, and he gave me a desk there,” he says. “Yen-Jie is almost like a father figure to me now.”

    A smashing lab

    One aim of Badea’s close-knit research group is to examine what happens after two particles are smashed together. The idea is that when researchers collide two heavy ions, the events that follow closely resemble what happened right after the Big Bang, potentially giving insight into the beginnings of the universe.

    “These are little bangs … but the Big Bang you only have one of,” he says. “And we can do many, many, many of [these little bangs].”

    Specifically, the lab is interested in a material that existed just moments after the Big Bang, called quark-gluon plasma — Badea describes it as melting a proton down into a soup. When researchers take two heavy nuclei and smash them together, they are confident that they are recreating that same kind of plasma. If they go a step smaller, colliding two protons instead of two nuclei, they observe an enhancement that looks like the presence of the plasma, but they’re not certain. Badea’s research takes it one step smaller — he looks at the tiniest known possible collision, between electrons and positrons, which are pieces of protons themselves.

    Most of the data for the lab’s research come from CERN’s Large Hadron Collider, where Badea worked for the last two summers.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    However, the LHC isn’t capable of colliding electrons and positrons. The only collider that did run electron-positron collisions closed several years ago.

    CERN Electron Positron Collider no longer operating

    Badea and Lee knew that if they wanted to study those collisions, they needed the archived data from that retired collider. It took months, but Lee finally got access to it around December 2016.

    “When we actually got the data, it was a moment of, ‘Okay, we can do this. We can actually make this happen,’” he recalls.

    A copious amount of data-cleaning and a few million lines of code later, Badea and his labmates began to make sense of the data. The whole project took two years, the first of which was spent replicating and confirming the calculations of the original researchers. They also found something interesting: When they looked at the particles after their collision, they did not see a signal like the one produced by the big particle collisions. In other words, smashing together these tiniest of particles does not create the proton-soup plasma, meaning that there is a set of conditions that were necessary to produce the plasma after the Big Bang and are now necessary to produce it at CERN. The team is submitting a short paper reporting their findings to Physical Review Letters and a longer one detailing the new techniques created for this analysis to the Journal of High Energy Physics.

    Game changer

    Before Badea discovered physics, his entire life was devoted to soccer. He was 14 when he was chosen for the U.S. Soccer Developmental Academy, which can act as a feeder program for the U.S. national team. After a year and a half, he became a starter. In his senior year, he felt like he was really flourishing — but he had a pretty big choice to make.

    “This was kind of around the time where I was deciding, do I want to go to a Division I school with … lesser academics, or do I want to try for something else?” he says.

    When Badea was offered a place in MIT’s class of 2019, he says, there was no question.

    “When I got in here, there was just some feeling where I thought, I can’t turn this down,” he says. “This is a once-in-a-lifetime.”

    During his time on MIT’s Division III soccer team, he’s had some major injuries, including a torn ACL, a torn adductor, a torn hamstring, and a strained IT band, that put him on the sidelines for months at a time. But this year, spending less time on the field gave him a chance to serve in a mentorship role for younger players.

    “It was a big maturing moment for me, to be a leader without being the focal point of a team,” he says.

    And, as his final season at MIT came to a close in October, he was healthy enough to finish his collegiate career on the field.

    Physics and future

    In his spare time, Badea has worked as a grader for the Department of Physics. He has developed his own method of giving feedback in which he focuses on errors in students’ thinking rather than their calculations. He has also gotten involved with peer tutoring and mentoring within his research group, and values the role he plays for younger students his lab.

    “Now that I’m a senior member in the group, there’s new undergrads that are coming up, so I get to be the mentors to them,” he says. “And so what Yen-Jie was to me, I get to be to them.”

    This year, he moved in to the house of his fraternity Phi Beta Epsilon, where he has “three really cool roommates.” Though he liked the quiet of his single room in Maseeh Hall, he enjoys living with people who have diverse interests. And he makes a point to exercise an hour and a half to two hours every day — he doesn’t think he’s missed a day since he’s been at MIT.

    Badea has just submitted his applications for PhD programs in physics. But he’s also taken up a humanities concentration in political science and is interested in how science can be used to support policymaking. For instance, the wildfires in his home state of California strike him as an issue that researchers in many disciplines could play a role in addressing.

    “In the physics department, you have some of the smartest people in the entire world,” he says. “If some of them put in some time into other things, a lot of change could happen.”

    See the full article here .


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  • richardmitnick 12:24 pm on January 8, 2019 Permalink | Reply
    Tags: A new planet HD 21749b, , , , , MIT,   

    From MIT News: “TESS discovers its third new planet, with longest orbit yet” 

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    From MIT News

    January 7, 2019
    Jennifer Chu

    1
    NASA’s TESS mission, which will survey the entire sky over the next two years, has already discovered three new exoplanets around nearby stars. Image: NASA’s Goddard Space Flight Center, edited by MIT News.

    2
    Using the first three months of publicly available data from NASA’s TESS mission, scientists at MIT and elsewhere have confirmed a new planet, HD 21749b — the third small planet that TESS has so far discovered. HD 21749b orbits a star, about the size of the sun, 53 light years away. Image: NASA/MIT/TESS

    Measurements indicate a dense, gaseous, “sub-Neptune” world, three times the size of Earth.

    NASA’s Transiting Exoplanet Survey Satellite, TESS, has discovered a third small planet outside our solar system, scientists announced this week at the annual American Astronomical Society meeting in Seattle.

    The new planet, named HD 21749b, orbits a bright, nearby dwarf star about 53 light years away, in the constellation Reticulum, and appears to have the longest orbital period of the three planets so far identified by TESS. HD 21749b journeys around its star in a relatively leisurely 36 days, compared to the two other planets — Pi Mensae b, a “super-Earth” with a 6.3-day orbit, and LHS 3844b, a rocky world that speeds around its star in just 11 hours. All three planets were discovered in the first three months of TESS observations.

    The surface of the new planet is likely around 300 degrees Fahrenheit — relatively cool, given its proximity to its star, which is almost as bright as the sun.

    “It’s the coolest small planet that we know of around a star this bright,” says Diana Dragomir, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research, who led the new discovery. “We know a lot about atmospheres of hot planets, but because it’s very hard to find small planets that orbit farther from their stars, and are therefore cooler, we haven’t been able to learn much about these smaller, cooler planets. But here we were lucky, and caught this one, and can now study it in more detail.”

    The planet is about three times the size of Earth, which puts it in the category of a “sub-Neptune.” Surprisingly, it is also a whopping 23 times as massive as the Earth. But it is unlikely that the planet is rocky and therefore habitable; it’s more likely made of gas, of a kind that is much more dense than the atmospheres of either Neptune or Uranus.

    “We think this planet wouldn’t be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy,” Dragomir says. “The planet likely has a density of water, or a thick atmosphere.”

    Serendipitously, the researchers have also detected evidence of a second planet, though not yet confirmed, in the same planetary system, with a shorter, 7.8-day orbit. If it is confirmed as a planet, it could be the first Earth-sized planet discovered by TESS.

    In addition to presenting their results at the AAS meeting, the researchers have submitted a paper to The Astrophysical Journal Letters.

    “Something there”

    Since it launched in April 2018, TESS, an MIT-led mission, has been monitoring the sky, sector by sector, for momentary dips in the light of about 200,000 nearby stars. Such dips likely represent a planet passing in front of that star.

    The satellite trains its four onboard cameras on each sector for 27 days, taking in light from the stars in that particular segment before shifting to view the next one. Over its two-year mission, TESS will survey nearly the entire sky by monitoring and piecing together overlapping slices of the night sky. The satellite will spend the first year surveying the sky in the Southern Hemisphere, before swiveling around to take in the Northern Hemisphere sky.

    The mission has released to the public all the data TESS has collected so far from the first three of the 13 sectors that it will monitor in the southern sky. For their new analysis, the researchers looked through this data, collected between July 25 and Oct. 14.

    Within the sector 1 data, Dragomir identified a single transit, or dip, in the light from the star HD 21749. As the satellite only collects data from a sector for 27 days, it’s difficult to identify planets with orbits longer than that time period; by the time a planet passes around again, the satellite may have shifted to view another slice of the sky.

    To complicate matters, the star itself is relatively active, and Dragomir wasn’t sure if the single transit she spotted was a result of a passing planet or a blip in stellar activity. So she consulted a second dataset, collected by the High Accuracy Radial velocity Planet Searcher, or HARPS, a high-precision spectrograph installed on a large ground-based telescope in Chile, which identifies exoplanets by their gravitational tug on their host stars.

    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.


    ESO/HARPS at La Silla

    “They had looked at this star system a decade ago and never announced anything because they weren’t sure if they were looking at a planet versus the activity of the star,” Dragomir says. “But we had this one transit, and knew something was there.”

    Stellar detectives

    When the researchers looked through the HARPS data, they discovered a repeating signal emanating from HD 21749 every 36 days. From this, they estimated that, if they indeed had seen a transit in the TESS data from sector 1, then another transit should appear 36 days later, in data from sector 3. When that data became publicly available, a momentary glitch created a gap in the data just at the time when Dragomir expected the second transit to occur.

    “Because there was an interruption in data around that time, we initially didn’t see a second transit, and were pretty disappointed,” Dragomir recalls. “But we re-extracted the data and zoomed in to look more carefully, and found what looked like the end of a transit.”

    She and her colleagues compared the pattern to the first full transit they had originally discovered, and found a near perfect match — an indication that the planet passed again in front of its star, in a 36-day orbit.

    “There was quite some detective work involved, and the right people were there at the right time,” Dragomir says. “But we were lucky and we caught the signals, and they were really clear.”

    They also used data from the Planet Finder Spectrograph, an instrument installed on the Magellan Telescope in Chile, to further validate their findings and constrain the planet’s mass and orbit.

    Carnegie Planet Finder Spectrograph on the Magellan Clay telescope at Las Campanas, Chile, Altitude 2,380 m (7,810 ft)

    Las Campanas Clay Magellan telescope, located at Carnegie’s Las Campanas Observatory, Chile, approximately 100 kilometres (62 mi) northeast of the city of La Serena, over 2,500 m (8,200 ft) high

    Once TESS has completed its two-year monitoring of the entire sky, the science team has committed to delivering information on 50 small planets less than four times the size of Earth to the astronomy community for further follow-up, either with ground-based telescopes or the future James Webb Space Telescope.

    NASA/ESA/CSA Webb Telescope annotated

    “We’ve confirmed three planets so far, and there are so many more that are just waiting for telescope and people time to be confirmed,” Dragomir says. “So it’s going really well, and TESS is already helping us to learn about the diversity of these small planets.”

    TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by Goddard. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes, and observatories worldwide are participants in the mission.

    See the full article here .


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  • richardmitnick 2:26 pm on January 4, 2019 Permalink | Reply
    Tags: , , , , , MIT   

    From MIT News: “Tiny satellites could be “guide stars” for huge next-generation telescopes” 

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    From MIT News

    January 4, 2019
    Jennifer Chu

    1
    In the coming decades, massive segmented space telescopes may be launched to peer even closer in on far-out exoplanets and their atmospheres. To keep these mega-scopes stable, MIT researchers say that small satellites can follow along, and act as “guide stars,” by pointing a laser back at a telescope to calibrate the system, to produce better, more accurate images of distant worlds. Image: Christine Daniloff, MIT

    Researchers design CubeSats with lasers to provide steady reference light for telescopes investigating distant planets.

    There are more than 3,900 confirmed planets beyond our solar system. Most of them have been detected because of their “transits” — instances when a planet crosses its star, momentarily blocking its light. These dips in starlight can tell astronomers a bit about a planet’s size and its distance from its star.

    Planet transit. NASA/Ames

    But knowing more about the planet, including whether it harbors oxygen, water, and other signs of life, requires far more powerful tools. Ideally, these would be much bigger telescopes in space, with light-gathering mirrors as wide as those of the largest ground observatories. NASA engineers are now developing designs for such next-generation space telescopes, including “segmented” telescopes with multiple small mirrors that could be assembled or unfurled to form one very large telescope once launched into space.

    NASA’s upcoming James Webb Space Telescope is an example of a segmented primary mirror, with a diameter of 6.5 meters and 18 hexagonal segments. Next-generation space telescopes are expected to be as large as 15 meters, with over 100 mirror segments.

    NASA/ESA/CSA Webb Telescope annotated

    One challenge for segmented space telescopes is how to keep the mirror segments stable and pointing collectively toward an exoplanetary system. Such telescopes would be equipped with coronagraphs — instruments that are sensitive enough to discern between the light given off by a star and the considerably weaker light emitted by an orbiting planet. But the slightest shift in any of the telescope’s parts could throw off a coronagraph’s measurements and disrupt measurements of oxygen, water, or other planetary features.

    Now MIT engineers propose that a second, shoebox-sized spacecraft equipped with a simple laser could fly at a distance from the large space telescope and act as a “guide star,” providing a steady, bright light near the target system that the telescope could use as a reference point in space to keep itself stable.

    In a paper published today in The Astronomical Journal, the researchers show that the design of such a laser guide star would be feasible with today’s existing technology. The researchers say that using the laser light from the second spacecraft to stabilize the system relaxes the demand for precision in a large segmented telescope, saving time and money, and allowing for more flexible telescope designs.

    “This paper suggests that in the future, we might be able to build a telescope that’s a little floppier, a little less intrinsically stable, but could use a bright source as a reference to maintain its stability,” says Ewan Douglas, a postdoc in MIT’s Department of Aeronautics and Astronautics and a lead author on the paper.

    The paper also includes Kerri Cahoy, associate professor of aeronautics and astronautics at MIT, along with graduate students James Clark and Weston Marlow at MIT, and Jared Males, Olivier Guyon, and Jennifer Lumbres from the University of Arizona.

    In the crosshairs

    For over a century, astronomers have been using actual stars as “guides” to stabilize ground-based telescopes.

    “If imperfections in the telescope motor or gears were causing your telescope to track slightly faster or slower, you could watch your guide star on a crosshairs by eye, and slowly keep it centered while you took a long exposure,” Douglas says.

    In the 1990s, scientists started using lasers on the ground as artificial guide stars by exciting sodium in the upper atmosphere, pointing the lasers into the sky to create a point of light some 40 miles from the ground. Astronomers could then stabilize a telescope using this light source, which could be generated anywhere the astronomer wanted to point the telescope.

    ESO VLT 4 lasers on Yepun

    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT.

    “Now we’re extending that idea, but rather than pointing a laser from the ground into space, we’re shining it from space, onto a telescope in space,” Douglas says. Ground telescopes need guide stars to counter atmospheric effects, but space telescopes for exoplanet imaging have to counter minute changes in the system temperature and any disturbances due to motion.

    The space-based laser guide star idea arose out of a project that was funded by NASA. The agency has been considering designs for large, segmented telescopes in space and tasked the researchers with finding ways of bringing down the cost of the massive observatories.

    “The reason this is pertinent now is that NASA has to decide in the next couple years whether these large space telescopes will be our priority in the next few decades,” Douglas says. “That decision-making is happening now, just like the decision-making for the Hubble Space Telescope happened in the 1960s, but it didn’t launch until the 1990s.’”

    Star fleet

    Cahoy’s lab has been developing laser communications for use in CubeSats, which are shoebox-sized satellites that can be built and launched into space at a fraction of the cost of conventional spacecraft.

    For this new study, the researchers looked at whether a laser, integrated into a CubeSat or slightly larger SmallSat, could be used to maintain the stability of a large, segmented space telescope modeled after NASA’s LUVOIR (for Large UV Optical Infrared Surveyor), a conceptual design that includes multiple mirrors that would be assembled in space.

    NASA Large UV Optical Infrared Surveyor (LUVOIR)

    Researchers have estimated that such a telescope would have to remain perfectly still, within 10 picometers — about a quarter the diameter of a hydrogen atom — in order for an onboard coronagraph to take accurate measurements of a planet’s light, apart from its star.

    “Any disturbance on the spacecraft, like a slight change in the angle of the sun, or a piece of electronics turning on and off and changing the amount of heat dissipated across the spacecraft, will cause slight expansion or contraction of the structure,” Douglas says. “If you get disturbances bigger than around 10 picometers, you start seeing a change in the pattern of starlight inside the telescope, and the changes mean that you can’t perfectly subtract the starlight to see the planet’s reflected light.”

    The team came up with a general design for a laser guide star that would be far enough away from a telescope to be seen as a fixed star — about tens of thousands of miles away — and that would point back and send its light toward the telescope’s mirrors, each of which would reflect the laser light toward an onboard camera. That camera would measure the phase of this reflected light over time. Any change of 10 picometers or more would signal a compromise to the telescope’s stability that, onboard actuators could then quickly correct.

    To see if such a laser guide star design would be feasible with today’s laser technology, Douglas and Cahoy worked with colleagues at the University of Arizona to come up with different brightness sources, to figure out, for instance, how bright a laser would have to be to provide a certain amount of information about a telescope’s position, or to provide stability using models of segment stability from large space telescopes. They then drew up a set of existing laser transmitters and calculated how stable, strong, and far away each laser would have to be from the telescope to act as a reliable guide star.

    In general, they found laser guide star designs are feasible with existing technologies, and that the system could fit entirely within a SmallSat about the size of a cubic foot. Douglas says that a single guide star could conceivably follow a telescope’s “gaze,” traveling from one star to the next as the telescope switches its observation targets. However, this would require the smaller spacecraft to journey hundreds of thousands of miles paired with the telescope at a distance, as the telescope repositions itself to look at different stars.

    Instead, Douglas says a small fleet of guide stars could be deployed, affordably, and spaced across the sky, to help stabilize a telescope as it surveys multiple exoplanetary systems. Cahoy points out that the recent success of NASA’s MARCO CubeSats, which supported the Mars Insight lander as a communications relay, demonstrates that CubeSats with propulsion systems can work in interplanetary space, for longer durations and at large distances.

    NASA/Mars InSight Lander

    Marco Cubesats in support of NASA Mars Insight Lander for radio relay

    Depiction of NASA JPL MarCo cubesat

    “Now we’re analyzing existing propulsion systems and figuring out the optimal way to do this, and how many spacecraft we’d want leapfrogging each other in space,” Douglas says. “Ultimately, we think this is a way to bring down the cost of these large, segmented space telescopes.”

    This research was funded in part by a NASA Early Stage Innovation Award.

    See the full article here .


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  • richardmitnick 2:01 pm on January 3, 2019 Permalink | Reply
    Tags: "Nuno Loureiro: Understanding turbulence in plasmas", , MIT, , ,   

    From MIT News: “Nuno Loureiro: Understanding turbulence in plasmas” 

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    From MIT News

    January 3, 2019
    Peter Dunn

    1
    “When we stimulate theoretically inclined minds by framing plasma physics and fusion challenges as beautiful theoretical physics problems, we bring into the game incredibly brilliant students,” says associate professor of nuclear science and engineering Nuno Loureiro. Photo: Gretchen Ertl

    Theoretical physicist’s focus on the complexity of plasma turbulence could pay dividends in fusion energy.

    Difficult problems with big payoffs are the life blood of MIT, so it’s appropriate that plasma turbulence has been an important focus for theoretical physicist Nuno Loureiro in his two years at the Institute, first as a assistant professor and now as an associate professor of nuclear science and engineering.

    New turbulence-related publications by Loureiro’s research group are contributing to the quest to develop nuclear fusion as a practical energy source, and to emerging astrophysical research that delves into the fundamental mechanisms of the universe.

    Turbulence is around us every day, when smoke rises through air, or milk is poured into coffee. While engineers can draw on substantial empirical knowledge of how it behaves, turbulence’s fundamental principles remain a mystery. Decades ago, Nobel laureate Richard Feynman ’39 referred to it as “the most important unsolved problem of classical physics” — and that still holds true today.

    But turbulence in air or coffee is a simple proposition compared to turbulence in plasma. Ordinary gases and liquids can be modeled as neutral fluids, but plasmas are electromagnetic media. Their turbulent behavior involves both the particles in the plasma (typically electrons and ions, but also electrons and positrons in so-called pair plasmas) and pervading electrical and magnetic fields. In addition, plasmas are often rarefied media where collisions are rare, creating an even more intricate dynamic.

    “There are several additional layers of complexity [in plasma turbulence] over neutral fluid turbulence,” Loureiro says.

    This lack of first-principles understanding is hindering the adaption of fusion for generating electricity. Tokamak-style fusion devices, like the Alcator C-Mod developed at MIT’s Plasma Science and Fusion Center (PSFC), where Loureiro’s research group is based, are a promising approach, and recent the spinout company Commonwealth Fusion Systems (CFS) is working to commercialize the concept. But fusion devices have yet to achieve net energy gain, in large part because of turbulence.

    Alcator C-Mod tokamak at MIT, no longer in operation

    Loureiro and his student Rogério Jorge, with co-author Professor Paolo Ricci from the École Polytechnique Fédérale de Lausanne, Switzerland, recently helped advance thinking in this area in a new paper, “Theory of the Drift-Wave Instability at Arbitrary Collisionality,” published in the journal Physical Review Letters.

    “This was amazing work by a fantastic student — a very complicated calculation that represents a qualitative advancement to the field,” Loureiro says.

    He explains that turbulence in tokamaks changes “flavor” depending on “where you are — at the periphery or near the core.”

    “Both are important, but periphery turbulence has important engineering implications because it determines how much heat reaches the plasma-facing components of the device,” Loureiro says. Preventing heat damage to materials, and maximizing operational life, are key priorities for tokamak developers.

    The paper offers a novel and more-robust description of turbulence in the tokamak periphery caused by low-frequency drift waves, which are a key source of that turbulence and regulators of plasma transport across magnetic fields. And because the computational framework is especially efficient, the approach can be easily extended to other applications. “I think it’s going to be an important piece of work for the fusion concepts that PSFC and CFS are trying to develop,” he says.

    A separate paper, “Turbulence in Magnetized Pair Plasmas,” which Loureiro co-authored with Professor Stanislav Boldyrev of the University of Wisconsin at Madison, puts forward the first theory of turbulence in pair plasmas. The work, published in The Astrophysical Journal Letters, was driven in part by last year’s unprecedented observations of a binary neutron star merger and other discoveries in astrophysics that suggest pair plasmas may be abundant in space — though none has been successfully created on Earth.

    “A variety of astrophysical environments are probably pair-plasma dominated, and turbulent,” notes Loureiro. “Pair plasmas are quite different from regular plasmas. In a normal electron-ion plasma, the ion is about 2,000 times heavier than the electron. But electrons and positrons have exactly the same mass, so there’s a whole range of behaviors that aren’t possible in a normal plasma and vice-versa.”

    Because computational calculations involving equal-weight particles are much more efficient, researchers often run pair-plasma numerical simulations and try to extrapolate findings to electron-ion plasmas.

    “But if you don’t understand how they’re the same or different from a theoretical point of view, it’s very hard to make that connection,” Loureiro points out. “By providing that theory we can help tell which characteristics are intrinsic to pair plasmas and which are shared. Looking at the building blocks may impact electron-ion plasma research too.”

    This theme of theoretical integration characterizes much of Loureiro’s work, and led to his being invited to present at a recent interdisciplinary event for plasma physicists and astrophysicists at New York City’s Flatiron Institute Center for Computational Astrophysics, an arm of a foundation created by billionaire James Simons ’58. It is also central to his role as a theorist within the MIT NSE ecosystem, especially on extremely complex challenges like fusion development.

    “There are people who are driven by technology and engineering, and others who are driven by fundamental mathematics and physics. We need both,” he explains. “When we stimulate theoretically inclined minds by framing plasma physics and fusion challenges as beautiful theoretical physics problems, we bring into the game incredibly brilliant students, people who we want to attract to fusion development but who wouldn’t have an engineer’s excitement about new advances in technology.

    “And they will stay on because they see not just the applicability of fusion but also the intellectual challenge,” he says. “That’s key.”

    See the full article here .


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  • richardmitnick 1:40 pm on January 3, 2019 Permalink | Reply
    Tags: "Controllable fast, A fundamental characteristic of electrons is their spin which points either up or down. A skyrmion is a circular cluster of electrons whose spins are opposite to the orientation of surrounding electro, , Dzyaloshinskii-Moriya interaction (DMI), Ferromagnets, MIT, , , , tiny magnetic bits"   

    From MIT News: “Controllable fast, tiny magnetic bits” 

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    From MIT News

    January 3, 2019
    Denis Paiste

    MIT researchers show how to make and drive nanoscale magnetic quasi-particles known as skyrmions for spintronic memory devices.

    1
    Work by researchers in the group of MIT materials science and engineering Professor Geoffrey Beach and colleagues in California, Germany, Switzerland and Korea, was featured on the covers of Nature Nanotechnology and Advanced Materials. Cover images reproduced with permission of the publishers.

    2
    Lucas Caretta (left) and Ivan Lemesh, graduate students in the lab of MIT professor of materials science and engineering Geoffrey Beach, each had a cover article in a peer-reviewed journal article in December. Their work is pioneering new directions for spintronic devices based on quasi-particles known as skyrmions. Photo: Denis Paiste/Materials Research Laboratory.

    For many modern technical applications, such as superconducting wires for magnetic resonance imaging, engineers want as much as possible to get rid of electrical resistance and its accompanying production of heat.

    It turns out, however, that a bit of heat production from resistance is a desirable characteristic in metallic thin films for spintronic applications such as solid-state computer memory. Similarly, while defects are often undesirable in materials science, they can be used to control creation of magnetic quasi-particles known as skyrmions.

    In separate papers published this month in the journals Nature Nanotechnology and Advanced Materials, researchers in the group of MIT Professor Geoffrey S.D. Beach and colleagues in California, Germany, Switzerland, and Korea, showed that they can generate stable and fast moving skyrmions in specially formulated layered materials at room temperature, setting world records for size and speed. Each paper was featured on the cover of its respective journal.

    For the research published in Advanced Materials [link is above], the researchers created a wire that stacks 15 repeating layers of a specially fabricated metal alloy made up of platinum, which is a heavy metal, cobalt-iron-boron, which is a magnetic material, and magnesium-oxygen. In these layered materials, the interface between the platinum metal layer and cobalt-iron-boron creates an environment in which skyrmions can be formed by applying an external magnetic field perpendicular to the film and electric current pulses that travel along the length of the wire.

    Notably, under a 20 milliTesla field, a measure of the magnetic field strength, the wire forms skyrmions at room temperature. At temperatures above 349 kelvins (168 degrees Fahrenheit), the skyrmions form without an external magnetic field, an effect caused by the material heating up, and the skyrmions remain stable even after the material is cooled back to room temperature. Previously, results like this had been seen only at low temperature and with large applied magnetic fields, Beach says.

    Predictable structure

    “After developing a number of theoretical tools, we now can not only predict the internal skyrmion structure and size, but we also can do a reverse engineering problem, we can say, for instance, we want to have a skyrmion of that size, and we’ll be able to generate the multi-layer, or the material, parameters, that would lead to the size of that skyrmion,” says Ivan Lemesh, first author of the Advanced Materials paper and a graduate student in materials science and engineering at MIT. Co-authors include senior author Beach and 17 others.

    A fundamental characteristic of electrons is their spin, which points either up or down. A skyrmion is a circular cluster of electrons whose spins are opposite to the orientation of surrounding electrons, and the skyrmions maintain a clockwise or counter-clockwise direction.

    “However, on top of that, we have also discovered that skyrmions in magnetic multilayers develop a complex through-thickness dependent twisted nature,” Lemesh said during a presentation on his work at the Materials Research Society (MRS) fall meeting in Boston on Nov. 30. Those findings were published in a separate theoretical study in Physical Review B in September.

    The current research shows that while this twisted structure of skyrmions has a minor impact on the ability to calculate the average size of the skyrmion, it significantly affects their current-induced behavior.

    Fundamental limits

    For the paper in Nature Nanotechnology [link is above], the researchers studied a different magnetic material, layering platinum with a magnetic layer of a gadolinium cobalt alloy, and tantalum oxide. In this material, the researchers showed they could produce skyrmions as small as 10 nanometers and established that they could move at a fast speed in the material.

    “What we discovered in this paper is that ferromagnets have fundamental limits for the size of the quasi-particle you can make and how fast you can drive them using currents,” says first author Lucas Caretta, a graduate student in materials science and engineering.

    In a ferromagnet, such as cobalt-iron-boron, neighboring spins are aligned parallel to one another and develop a strong directional magnetic moment. To overcome the fundamental limits of ferromagnets, the researchers turned to gadolinium-cobalt, which is a ferrimagnet, in which neighboring spins alternate up and down so they can cancel each other out and result in an overall zero magnetic moment.

    “One can engineer a ferrimagnet such that the net magnetization is zero, allowing ultrasmall spin textures, or tune it such that the net angular momentum is zero, enabling ultrafast spin textures. These properties can be engineered by material composition or temperature,” Caretta explains.

    In 2017, researchers in Beach’s group and their collaborators demonstrated experimentally that they could create these quasi-particles at will in specific locations by introducing a particular kind of defect in the magnetic layer.

    “You can change the properties of a material by using different local techniques such as ion bombardment, for instance, and by doing that you change its magnetic properties,” Lemesh says, “and then if you inject a current into the wire, the skyrmion will be born in that location.”

    Adds Caretta: “It was originally discovered with natural defects in the material, then they became engineered defects through the geometry of the wire.”

    They used this method to create skyrmions in the new Nature Nanotechnology [link is above] paper.

    The researchers made images of the skyrmions in the cobalt-gadolinium mixture at room temperature at synchrotron centers in Germany, using X-ray holography. Felix Büttner, a postdoc in the Beach lab, was one of the developers of this X-ray holography technique. “It’s one of the only techniques that can allow for such highly resolved images where you make out skyrmions of this size,” Caretta says.

    These skyrmions are as small as 10 nanometers, which is the current world record for room temperature skyrmions. The researchers demonstrated current driven domain wall motion of 1.3 kilometers per second, using a mechanism that can also be used to move skyrmions, which also sets a new world record.

    Except for the synchrotron work, all the research was done at MIT. “We grow the materials, do the fabrication and characterize the materials here at MIT,” Caretta says.

    Magnetic modeling

    These skyrmions are one type of spin configuration of electron spins in these materials, while domain walls are another. Domain walls are the boundary between domains of opposing spin orientation. In the field of spintronics, these configurations are known as solitons, or spin textures. Since skyrmions are a fundamental property of materials, mathematical characterization of their energy of formation and motion involves a complex set of equations incorporating their circular size, spin angular momentum, orbital angular momentum, electronic charge, magnetic strength, layer thickness, and several special physics terms that capture the energy of interactions between neighboring spins and neighboring layers, such as the exchange interaction.

    One of these interactions, which is called the Dzyaloshinskii-Moriya interaction (DMI), is of special significance to forming skyrmions and arises from the interplay between electrons in the platinum layer and the magnetic layer. In the Dzyaloshinskii-Moriya interaction, spins align perpendicular to each other, which stabilizes the skyrmion, Lemesh says. The DMI interaction allows for these skyrmions to be topological, giving rise to fascinating physics phenomena, making them stable, and allowing for them to be moved with a current.

    “The platinum itself is what provides what’s called a spin current which is what drives the spin textures into motion,” Caretta says. “The spin current provides a torque on the magnetization of the ferro or ferrimagnet adjacent to it, and this torque is what ultimately causes the motion of the spin texture. We’re basically using simple materials to realize complicated phenomena at interfaces.”

    In both papers, the researchers performed a mix of micromagnetic and atomistic spin calculations to determine the energy required to form skyrmions and to move them.

    “It turns out that by changing the fraction of a magnetic layer, you can change the average magnetic properties of the whole system, so now we don’t need to go to a different material to generate other properties,” Lemesh says. “You can just dilute the magnetic layer with a spacer layer of different thickness, and you will wind up with different magnetic properties, and that gives you an infinite number of opportunities to fabricate your system.”

    Precise control

    “Precise control of creating magnetic skyrmions is a central topic of the field,” says Jiadong Zang, an assistant professor of physics at the University of New Hampshire, who was not involved in this research, regarding the Advanced Materials paper. “This work has presented a new way of generating zero field skyrmions via current pulse. This is definitely a solid step towards skyrmion manipulations in nanosecond regime.”

    Commenting on the Nature Nanotechnology report, Christopher Marrows, a professor of condensed matter physics at the University of Leeds in the United Kingdom says: “The fact that the skyrmions are so small but can be stabilized at room temperature makes it very significant.”

    Marrows, who also was not involved in this research, noted that the Beach group had predicted room temperature skyrmions in a Scientific Reports paper earlier this year and said the new results are work of the highest quality. “But they made the prediction and real life does not always live up to theoretical expectations, so they deserve all the credit for this breakthrough,” Marrows says.

    Zang, commenting on the Nature Nanotechnology paper, adds: “A bottleneck of skyrmion study is to reach a size of smaller than 20 nanometers [the size of state-of-art memory unit], and drive its motion with speed beyond one kilometer per second. Both challenges have been tackled in this seminal work.

    “A key innovation is to use ferrimagnet, instead of commonly used ferromagnet, to host skyrmions,” Zang says. “This work greatly stimulates the design of skyrmion-based memory and logic devices. This is definitely a star paper in the skyrmion field.”

    Racetrack systems

    Solid-state devices built on these skyrmions could someday replace current magnetic storage hard drives. Streams of magnetic skyrmions can act as bits for computer applications. “In these materials, we can readily pattern magnetic tracks,” Beach said during a presentation at MRS.

    These new findings could be applied to racetrack memory devices, which were developed by Stuart Parkin at IBM. A key to engineering these materials for use in racetrack devices is engineering deliberate defects into the material where skyrmions can form, because skyrmions form where there are defects in the material.

    “One can engineer by putting notches in this type of system,” said Beach, who also is co-director of the Materials Research Laboratory (MRL) at MIT. A current pulse injected into the material forms the skyrmions at a notch. “The same current pulse can be used to write and delete,” he said. These skyrmions form extremely quickly, in less than a billionth of a second, Beach says.

    Says Caretta: “To be able to have a practical operating logic or memory racetrack device, you have to write the bit, so that’s what we talk about in creating the magnetic quasi particle, and you have to make sure that the written bit is very small and you have to translate that bit through the material at a very fast rate,” Caretta says.

    Marrows, the Leeds professor, adds: “Applications in skyrmion-based spintronics, will benefit, although again it’s a bit early to say for sure what will be the winners among the various proposals, which include memories, logic devices, oscillators and neuromorphic devices,”

    A remaining challenge is the best way to read these skyrmion bits. Work in the Beach group is continuing in this area, Lemesh says, noting that the current challenge is to discover a way to detect these skyrmions electrically in order to use them in computers or phones.

    “Yea, so you don’t have to take your phone to a synchrotron to read a bit,” Caretta says. “As a result of some of the work done on ferrimagnets and similar systems called anti-ferromagnets, I think the majority of the field will actually start to shift toward these types of materials because of the huge promise that they hold.”

    See the full article here .


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  • richardmitnick 11:40 am on January 2, 2019 Permalink | Reply
    Tags: Anna Frebel, , , , , HE 1327-2326, HE 1523-0901 a red giant star in the Milky Way galaxy, low “metallicity Second-generation stars identified giving clues about their predecessors, MIT,   

    From MIT News: Women in STEM-“Anna Frebel is searching the stars for clues to the universe’s origins” 

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    From MIT News

    January 1, 2019
    Jennifer Chu

    1
    Anna Frebel. Image: Bryce Vickmark

    MIT astronomer and writer investigates ancient starlight and shares her excitement about the cosmos.

    In August 2002, Anna Frebel pressed pause on her undergraduate physics studies in Germany and spent her entire life savings on a plane ticket to take her halfway around the world, to a mountaintop observatory just outside Canberra, Australia.

    She spent the next five months volunteering at the Australian National University Research School of Astronomy and Astrophysics, where astronomers had regular access to a set of world-class telescopes set atop Mount Stromlo.

    On Jan. 18, 2003, brushfires that had been burning for weeks in the surrounding forest suddenly advanced toward Canberra, whipped up by a dry, scorching wind.

    “The fire front just swept in, and it marched at about six to seven miles an hour, and it just rode right into the city. The observatory was the first to fall,” recalls Frebel, who watched the calamity from the opposite end of Canberra.

    The fires obliterated the observatory’s historic telescopes, along with several administrative buildings and even some homes of researchers living on the mountainside.

    “It was a pretty big shock,” Frebel says. “But tragedy also brings out community, and we were all helping each other, and it really bonded us together.”

    As the campus set to work clearing the ash and rebuilding the facility, Frebel decided to extend her initially one-year visit to Australia — a decision that turned out to be career-making.

    “I wasn’t going to be deterred by a burned-down observatory,” says Frebel, who was granted a tenure position this year in MIT’s Department of Physics.

    Frebel’s star

    Soon after the fires subsided, Frebel accepted an offer by the Australian National University to pursue a PhD in astronomy. She chose to focus her studies on a then-fledgling field: the search for the universe’s oldest stars.

    It’s believed that, immediately after the Big Bang exploded the universe into existence, clouds of hydrogen, helium, and lithium coalesced to form the very first generation of stars. These incredibly massive stellar pioneers grew out of control and quickly burned out as supernovas.

    To sustain their enormous luminosities, atoms of hydrogen and helium smashed together to create heavier elements in their cores, considered to be the universe’s first “metals” — a term in astronomy used to describe all elements that are heavier than hydrogen and helium. These metals in turn forged the second generation of stars, which researchers believe formed just half a billion years after the Big Bang.

    Since then, many stellar generations have populated the night sky, containing ever more abundant metals. Astronomers suspect, however, that those early, second-generation stars can still be found in some pockets of the universe, and possibly even in our own Milky Way.

    Frebel set out to find these oldest stars, also known as “metal-poor” stars. One of her first discoveries was HE 1327-2326, which contained the smallest amount of iron ever known, estimated at about 1/400,000 that of the Earth’s sun. Given this extremely low “metallicity,” the star was likely a second-generation star, born very shortly after the Big Bang. Until 2014, Frebel’s star remained the record-holder for the most metal-poor star ever discovered.

    The results were published in 2005 in Nature, with Frebel, then just two years into her PhD, as lead author.

    A star turn

    Frebel went on to work as a postdoc at the University of Texas at Austin, and later the Harvard-Smithsonian Center for Astrophysics, where she continued to make remarkable insights into the early universe. Most notably, in 2007, she discovered HE 1523-0901, a red giant star in the Milky Way galaxy. Frebel estimated the star to be about 13.2 billion years old — among the oldest stars ever discovered and nearly as old as the universe itself.

    In 2010, she unearthed a similarly primitive star in a nearby galaxy, that appeared to have the exact same metallic content as some of the old stars she had observed in the outskirts of our own Milky Way. This seemed to suggest, for the first time, that young galaxies like the Milky Way may “cannibalize” nearby, older galaxies, taking in their ancient stars as their own.

    “A lot more detail has come to light in the last 10 years or so, and now we’re asking questions like, not just whether these objects are out there, but exactly where did they form, and how,” Frebel says. “So the puzzle is filling in.”

    In 2012, she accepted an offer to join the physics faculty at MIT, where she continues to assemble the pieces to the early universe’s history. Much of her research is focused on analyzing stellar observations taken by the twin Magellan telescopes at the Las Campanas Observatory, in Chile.

    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

    Frebel’s group makes the long trek to the observatory about three times per year to collect light from stars in the Milky Way and small satellite dwarf galaxies.

    Once they arrive at the mountaintop observatory, the astronomers adapt to a night owl’s schedule, sleeping through the day and rising close to dinner time. Then, they grab a quick bite at the observatory’s lodge before heading up the mountainside to one of the two telescopes, where they remain into the early morning hours, collecting streams of photons from various stars of interest.

    On nights when bad weather makes data collection impossible, Frebel reviews her data or she writes — about the solitary, sleep-deprived experience of observatory work; the broader search for the universe’s oldest stars; and most recently, about an overlooked scientific heroine in nuclear physics.

    Engaging with the public

    In addition to her academic work, Frebel makes a point of reaching out to a broader audience, to share her excitement in the cosmos. In one of many essays that she’s penned for such popular magazines as Scientific American, she describes the satisfied weariness following a long night’s work:

    “Already I am imagining myself drawing the thick, sun-proof shades on my window and resting my head against my pillow. The morning twilight cloaks the stars overhead, but I know they are there — burning as they have for billions of years.”

    In 2015, she published her first book, Searching for the Oldest Stars: Ancient Relics from the Early Universe. And just last year, she wrote and performed a 12-minute play about the life and accomplishments of Lise Meitner, an Austrian-Swedish physicist who was instrumental in discovering nuclear fission. Meitner, who worked for most of her career in Berlin, Germany, fled to Sweden during the Nazi occupation. There, she and her long-time collaborator Otto Hahn found evidence of nuclear fission. But it was Hahn who ultimately received the Nobel Prize for the discovery.

    “Scientifically, [Meitner] is absolutely in line with Marie Curie, but she was never recognized appropriately for her work,” Frebel says. “She should be a household name, but she isn’t. So I find it very important to help rectify that.”

    Frebel has given a handful of performances of the play, during which she appears in the first half, dressed in costume as Meitner. In the second half, she appears as herself, explaining to the audience how Meitner’s revelations influence astronomers’ work today.

    Getting into character is nothing new for Frebel, who, as a high school student in Gottingen, Germany, took on multiple roles in the school plays. She also took part in what she calls the “subculture of figure-rollerskating” — a competitive sport that is analogous to figure-skating, only on roller skates. During that formative time, Frebel partly credits her mother for turning her focus to science and to the women who advanced their fields.

    “When I was a teenager, my mom gave me a lot of biographies of women scientists and other notable women, and I still have a little book of Lise Meitner from when I was around 13,” Frebel says. “So I have been very familiar with her, and I do work basically on the topic that she was interested in. So I’m one of her scientific daughters.”

    See the full article here .


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    Please help promote STEM in your local schools.


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  • richardmitnick 11:04 am on January 2, 2019 Permalink | Reply
    Tags: , , MIT, , Physicists record “lifetime” of graphene qubits, , ,   

    From MIT News: “Physicists record ‘lifetime’ of graphene qubits” 

    MIT News
    MIT Widget

    From MIT News

    December 31, 2018
    Rob Matheson

    1
    Researchers from MIT and elsewhere have recorded the “temporal coherence” of a graphene qubit — how long it maintains a special state that lets it represent two logical states simultaneously — marking a critical step forward for practical quantum computing. Stock image

    First measurement of its kind could provide stepping stone to practical quantum computing.

    Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit — meaning how long it can maintain a special state that allows it to represent two logical states simultaneously. The demonstration, which used a new kind of graphene-based qubit, represents a critical step forward for practical quantum computing, the researchers say.

    Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1. But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

    The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

    Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks. Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing.

    In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials. These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

    The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

    “Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT. “In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

    There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

    A pristine graphene sandwich

    Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum). In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

    But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

    To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage. These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

    For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches. The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

    When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene. The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

    How voltage helps

    The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip. “Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

    Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

    For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

    But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 1:55 pm on December 28, 2018 Permalink | Reply
    Tags: Exploring New England's coastal ecosystems in the dead of winter, MIT, MIT Sea Grant   

    From MIT News: “Exploring New England’s coastal ecosystems in the dead of winter” 

    MIT News
    MIT Widget

    From MIT News

    December 27, 2018
    Mary Beth O’Leary

    1
    Valerie Muldoon (left), a third-year mechanical engineering student, and biological engineering student Jenna Melanson explore a coastal ecosystem during a field trip to Odiorne Point State Park in New Hampshire. Image courtesy of MIT Sea Grant

    2
    Mechanical engineering alumna Jorlyn Le Garrec ’17 uses a hydrophone to measure the sounds of a rocky shore community. Image courtesy of MIT Sea Grant

    In early January 2018, a nor’easter pummeled the East Coast. A record-breaking high tide rendered many streets in Boston impassable and seawater rushed down Seaport Boulevard in Boston’s Seaport District. A deluge of water poured down the steps leading down to the Aquarium subway station, forcing it to close.

    Less than a week later, in a dry classroom on MIT’s campus, a group of students discussed how coastal cities like Boston can cope with worsening floods due to rising sea levels.

    “We live in a coastal city, so obviously we are being significantly impacted by sea level rise,” says Valerie Muldoon, a third-year mechanical engineering student. “We talked about the bad nor’easter earlier in January and brainstormed ways to mitigate the flooding.”

    Muldoon and her fellow students were enrolled in 2.981 (New England Coastal Ecology), a class that meets during MIT’s Independent Activities Period. The course is offered through the MIT Sea Grant College Program, which is affiliated with MIT’s Department of Mechanical Engineering.

    MIT Sea Grant instructors Juliet Simpson, a research engineer, and Carolina Bastidas, a research scientist, use the four-week class to introduce students to the biological makeup of coastal ecosystems, to the crucial role these areas play in protecting the environment, and to the effects human interaction and climate change have had on them.

    “We want to give a taste of coastal communities in New England to the students at MIT — especially those who come from abroad or other parts of the U.S.,” says Bastidas, a marine biologist who focuses her research primarily on coral and oyster reefs.

    Muldoon, who is a double minor in energy studies and environment and sustainability, says she was “so excited to see a Course 2 class on coastal ecology.”

    “I’m passionate about protecting the environment, so the topic really resonated with me,” she says.

    The course begins with an introduction to the different types of coastal ecosystems found in the New England area, such as rocky intertidal regions, salt marshes, eelgrass meadows, and kelp forests. In addition to providing an overview of the makeup of each environment, the course instructors also discuss the physiology of the countless organisms who live in them.

    Halfway through the course, students learn about how human impacts like climate change, eutrophication, and increased development have affected coastal habitats.

    “We focus on climate change as it impacts coastal communities like rocky shores and salt marshes,” says Simpson, a coastal ecologist who studies how plants and algae respond to human interference. “There are a lot of interesting implications for sea level rise for intertidal organisms.”

    Sea level rise, for example, has forced organisms that live in salt marshes to migrate upland. Changes in both water and air temperature also have a drastic effect on the inhabitants of coastal regions.

    “As temperatures rise, all of those organisms are going to need to adapt or the communities are going to change, possibly dramatically,” explains Simpson.

    Protecting coastal ecosystems has far reaching implications that go beyond the animals and plants that live there, because they offer a natural defense against climate change. Many coastal are natural hot spots for carbon capture and sequestration. Salt marshes and seagrass meadows all capture vast amounts of carbon that can be stored for several thousand years in peat.

    “I was shocked at how much carbon the plants in these ecosystems can hold through sequestration,” recalls Muldoon.

    Protecting these areas is essential to continue this natural sequestration of carbon and prevent carbon already stored there from leaking out. Coastal ecosystems are also instrumental in protecting coastal cities, like Boston, from flooding due to sea level rise.

    “We talk about the ecology of coastal cities and how flooding from storms and sea level rise impacts human communities,” adds Simpson.

    The class culminates in a field trip to Odiorne Point State Park in New Hampshire, where students get to interact with the communities they’ve learned about. Using fundamental techniques in ecology, students collect data about the species living in the salt marsh and rocky shore nearby.

    Bastidas and Simpson will expand the class’ scope beyond New England in a new course — 2.982 (Ecology and Sustainability of Coastal Ecosystems) — which will be offered in fall 2019.

    While the effects of climate change on coastal ecosystems often paint a dire picture, the instructors want students to focus on the positive.

    “Rather than have students focus on the gloom and doom aspect, we want to encourage them to come up with novel solutions for dealing with climate change and carbon emissions,” adds Bastidas.

    Muldoon sees a special role for mechanical engineers like herself in developing such solutions.

    “I think it’s so important for mechanical engineering students to take classes like this one because we are definitely going to be needed to help mitigate the problems that come with sea level rise,” she says.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

     
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